1. Field of the Invention
The present invention relates to a radiation detection system used for a diagnosis in a hospital, a radiation image pick-up device preferably used for an industrial non-destructive inspection, a radiation image pick-up method and a program.
2. Related Background Art
At present, a film system for irradiating a patient with X-rays and exposing its transmitted X-ray image to a film is a main stream of an X-ray still image photographing system in medical treatment. A film is widely spread because it has a function for displaying and recording information, a large area and a high gradation characteristic and is lightweight and easily handled.
There is a tomography photographing method as one of photographing methods using a film. FIG. 15 is a schematic view showing a conventional tomography photographing method using a film. A point F denotes the position of the focus of an X-ray generation source. The X ray from the point F passing through a point O in an objects to be detected (patient) is irradiated to a point S on a film face. That is, the points F, O and S are on a straight line. Then, the points F, O and S are exposed to the film while keeping the points F, O and S on the straight line and moving the X-ray source and the film in parallel with the tomography plane to be photographed. In this case, the X-ray source and film are moved in directions opposite to each other. By performing the above photographing, the tomography plane parallel with the film including the point O is photographed to the tomography plane. This method is generally referred to as a tomography photographing method. In the case of the example shown in FIG. 15, an X-ray tomogram of a tomography plane A including the point O, that is, the tomography plane A for dividing the interval between the X ray and the film at D:d.
In this case, a mechanism from which the X-ray tomogram of the tomography plane A is obtained is described. In the case of the example shown in FIG. 15, a relation of LF1F2/LS1S2=D/d is effected between the length LF1F2 of a segment F1F2 and the length LS1S2 of a segment S1S2 and a relation of LF1F2/LT1T2=D/d is effected between LF1F2 and the length LT1T2 of a segment T1T2. Points S1 and S2 are projection points of the point O from points F1 and F2. Points T1 and T2 are projection points of the point O′ from points F1 and F2. Moreover, a relation of LS1S2=LT1T2 is also effected. That is, projection images of the points O and O′ are uniquely reflected on the same film face. That is, it is possible to photograph a tomography image connecting the point O with the point O′ parallel with the film.
In the case of a point Z separate from the tomography plane A by a distance h to the X-ray source side, the projected image of the point Z moves from a point U1 up to a point U2 in accordance with the movement of the X-ray source. In this case, a relation of LF1F2/LU1U2=(D−h)/(d+h) is effected between LS1S2 and the length LU1U2 of a segment U1U2 but LF1F2 does not become equal to LU1U2 (LF1F2<LF1F2). As a result, the projection image of the point Z is not reflected on the film as a point but it is projected as the linear image of a length (LF1F2−LF1F2). Therefore, the image of an object to be detected (patient) present out of the tomography plane parallel with the film face including the points O and O′ like the point Z becomes a linearly fuzzy image but it is not reflected on the film. This is the principle of the tomography photographing method. FIG. 15 shows a tomography plane for dividing an X-ray source and a film into D:d in an objects to be detected (patient). However, it is possible to obtain an optional tomography image by previously selecting a positional relation between an X-ray source, patient and film.
Moreover, a request for digitization of an X-ray image has been recently raised in hospitals. For example, instead of a film an X-ray image pick-up device is started to be used in which X-ray detection devices (solid image pick-up devices) for respectively converting an X-ray dose into an electrical signal are arranged like a two-dimensional array. According to this X-ray image pick-up device, it is possible to instantaneously transmit information to a distant place because an X-ray image can be replaced to digital information. Therefore, for example, it is possible to receive an advanced diagnosis equal to that of a university hospital at an urban center even in a local area. Moreover, by avoiding use of a film, there is an advantage that it is possible to omit a film storing space in a hospital. Then, by using a superior image processing technique in future, a method is expected which automatically diagnoses a patient by using a computer not through a radiation doctor.
In recent years, a radiation image pick-up device capable of photographing a static image is practically used by using the fabrication techniques of an amorphous silicon thin-film semiconductor for a solid image pick-up device. Moreover, change to a large area exceeding 40-cm square covering the region of the chest of a human body is realized.
Furthermore, because the fabrication process is comparatively easy, it is expected to provide an inexpensive detector in future. Furthermore, because it is possible to fabricate amorphous silicon on a thin glass of 1 mm or less, there is an advantage that it is possible to fabricate the detector by greatly deceasing the detector in thickness and weight. Japanese Patent Application Laid-Open No. 8-116044 discloses a radiation image pick-up device using the above amorphous silicon thin-film semiconductor.
However, in the case of a tomography photographing method using a film, though it is possible to optionally decide a tomography plane to be obtained by previously selecting a positional relation between an X-ray source, film and object to be detected (patient), the number of tomograms obtained through one-time photographing is only one. That is, to obtain other tomography plane, it is necessary to perform photographing once more. Moreover, when a desired tomography image is not obtained, there is a case in which retry of photographing is inevitably selected again. This represents that the dosage of exposure to radiation increases for a patient and this is not preferable. Furthermore, the exposure time to a film generally requires several seconds in the case of the tomography photographing method. Therefore, a tomography image around the heart of the patient frequently becomes unclear in a chest tomography image due to the movement of the heat in an exposure period or the movement of breathing of the patient and it is difficult to obtain a preferably tomogram. Moreover, in the case of a method using a film not applied only to the tomography photographing method, many problems are left on management and operation in a hospital by including a problem on a film storage space and a problem that a lot of time is required to search a necessary patient film out of a great number of films in a hospital.
Furthermore, as described above, an X-ray image pick-up device provided with a solid image pick-up element is also developed. However, it is not changed that the number of tomograms obtained through one-time photographing is only one similarly to the case of using a film.